Make the version history view clearer

Is your feature request related to a problem? Please describe.
When you open the version history, and pick different older versions to check in the viewer on the left, there's no clear indication whether you're looking at an older version, and which one it is.
(currently there's a bug in online that the version history is shown in edit mode, which will be fixed shortly)

Describe the solution you'd like
Perhaps on the NC sidebar the line of the currently opened version should be highlighted, and/or the document details in the top side of the sidebar should be updated (as a smaller note, the preview doesn't seem to be useful in this case).

In addition/alternatively, online could also indicate in some way that you're looking at the version history, and which time the currently viewed state is from.
@pedropintosilva, what are your thoughts on this from a UX perspective?

Screenshot:

Start with the version history viewer and the NC sidebar, reproducing the behavior described in the issue and comparing it with the revision_picker screenshot. Define the indication for the selected older version and its time, then verify that the viewer and online mode clearly identify the historical state.